Subject:
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Single acting pneumatics with spring return
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Newsgroups:
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lugnet.technic, lugnet.robotics
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Date:
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Wed, 6 Mar 2002 17:21:28 GMT
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Viewed:
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1501 times
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Hello again,
I think I should have another go at this... I wanted to say "Check
this out, I found an interesting application for the old pneumatic
cylinders" What it came out sounding like was "Mr. Soh was wrong! Look
at me prove him wrong!"
Sorry about that. That wasn't my point. Anyway, If you have a look at
the links I posted earlier, you can see how I used the old red
cylinder asd a single acting cylinder with spring return:
http://www.ecf.utoronto.ca/~stehlik/images/ideas/pneumatics/old3.jpg
This type of pneumatic cylinder is very common in industry, as it
needs only one air line, and uses half the amount of air. To do this
with Lego, the only trick was putting elastics around the piston to
provide the spring return, and plugging up the unused port on the
valve. Actually, this same thing can be done with the new cylinders,
just don't connect a hose to the top port. The old style cylinders
just offer more speed and less friction. Originally, in the old
pneumatics system the air would be pumped in to extend the piston, and
the air would be sucked out to retract it. As several people have
pointed out, the suction does not work too well to pull the cylinders
back. Correct me if I am wrong, but this type of 'suction retraction'
is not commonly used in industry. I found that spring return is much
more effective, and you don't have to bother with the suction at all.
About the vacuum tanks... I won't beat this point to death, but I have
a few thoughts. According to the laws of phsics, gas flows from a high
pressure region to a low pressure region. When you compress air into a
tank, you are essentially creating a high pressure region. The air in
the tank will be at slightly higher pressure than atmospheric, so it
want to flow out of the tank. Now, lets do the opposite thing with a
suction pump: By pumping air out of the tank, you create a low
pressure region. This is by no means a vacuum, since you can not
remove all of the air with a lego pump, but describing it as a vacuum
tank seems to make sense. Since the air outside of the tank is at
atmospheric pressure, and inside the tank is at a lower pressure, the
air want to flow into the tank. Its really just the opposite of
compressing air. Now, in both cases, the air will move only as long as
the pressure difference is maintained. So if you pump up an air tank,
you can extend and retract a cylinder a few times until the pressure
in the tank drops to atmospheric pressure. With the low pressure tank,
you can suck air into it until the pressure increases to atmospheric
pressure. So... my window walker can climb happily away as long as the
tanks have a lower than atmospheric pressure in them. If I pump most
of the air out to start, the robot can climb about 6 steps before
needing a recharge. I suppose it would work without the air tanks, but
not as well:)
Rob
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Message has 2 Replies:
Message is in Reply To:
 | | Pneumatics: the old and the new
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| Hello pneumatics fans, I have been working a lot with pneumatics lately, and have made some interesting discoveries. I think the most notable is a method of using the old style red cylinders with the new pneumatics system. I came across this as I (...) (23 years ago, 1-Mar-02, to lugnet.technic, lugnet.robotics)
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